Field of the Invention
The invention relates to a cover device for covering particularly open liquid surfaces, such as ponds, lakes or pools, having a shell defining an inner cavity, and the inner cavity is filled at least partly with a liquid. The invention also relates to a blanket formed by several cover devices according to the invention on the surface of a pond or pool.
Brief Description of the Related Art
Different kinds of open air industrial ponds need to be covered to prevent e.g. sunlight penetration and consequent algae formation or growing weeds, liquid loss through evaporation, to maintain higher water temperature in winter, or waterfowl fatalities in cases of both hazardous liquids stored and airport fire water ponds situated near the runways attracting fowls in the vicinity of air-bound planes. A very conventional solution has been netting. Published patent document US 2012285106 (A1) discloses a bird deterrent for preventing birds from flying into a reflective surface e.g. a glass surface, comprising a mesh having a first portion and a second portion, first and second support beams coupled to the first and second portions, respectively; first and second sets of suction cups coupled to the first and second support beams, respectively; and wherein the first and second sets of suction cups are slidably coupled to the first and second support beams, respectively, and configured to removably attach to a glass surface. It is clear, however, using this solution in case of a large liquid surface, like a pond or pool, is too expensive to build and maintain and will obviously be damaged by winter storms, and yet fails to camouflage the liquid surface from waterfowls.
Published Chinese utility model CN 202555020 discloses a full-light covered top type device for a mud storing pond. The device mainly solves the problem that an existing mud storing pond cannot normally operate due to freezing in winter and is characterized in that top beams are connected with the top of a vertical column, the top beams in arc shapes are parallel to each other, evenly distributed, and connected through transverse beams, and the outer surfaces of the top beams are covered by sunlight plates. Although this full-light covered top type device for the mud storing pond is strong in cold resistance capacity, it is very expensive to establish and is alien from an ideal heat insulating and bird repelling solution as well.
These problems have been attempted to solve by floating ball blankets providing a highly effective solution to difficult liquid storage problems above mainly in petrochemical, metal treatment and air-transport industries (see: www.euro-matic.com). By placing a sufficient quantity of hollow plastic balls onto the surface of a liquid, the balls automatically arrange themselves into a close packed formation. In a single layer on the liquid surface they virtually cover over 91% of the surface area, greatly reducing sunlight penetration and therefore liquid evaporation. The thermal insulating qualities of such balls also assist in maintaining winter operating temperatures of the water. Such a high surface coverage provides an extremely effective barrier and significantly reduces the mass and heat transfer mechanisms operating between the liquid and surrounding environment. A thermal insulation barrier is achieved through the air held in each ball and the poor heat conductivity of plastic. The air pockets between the balls, although not sealed, also contribute to this cellular insulation system which dramatically reduces heat loss. The low liquid surface area exposed to atmosphere dramatically reduces liquid loss through evaporation, odor release to the atmosphere and also conversely prevents surface absorption of oxygen.
Yet a blanket of balls presents no impediment to product dipping or equipment which has to move through the liquid surface; the balls are pushed aside, but quickly reform their cover as the equipment moves forward or products are lifted away from the tank. The balls rise and fall with liquid level within ponds or storage tanks, and also provide a constant cover over liquids held in reservoirs with sloping sides. If the liquid level falls, causing the surface area to shrink, the balls simply stack in a double layer; they automatically spread themselves into a single layer again as the level rises.
However, this blanket of cover balls has some disadvantages. In almost all open air industrial applications the balls consisting the covering blanket may drift into a limited surface area of the pond, due to strong or even stormy winds, or they might also be blown out from the pond. This phenomenon can be eliminated by applying balls partly filled with a liquid, e.g. water, but both producing and transporting of balls filled at least partly with water incur extended costs.